Telephone and call signal system



A. B. CLARK.

TELEPHONE AND CALL SIGNAL SYSTEM.

APPLICATION FILED SEPT. 20, l9l8.

Patented Mar. 15, 1921.

'INVENTYOR. .43. Clark 4 z. 5

. .ATTOILNEY.

UNITED STATES PATENT OFFICE.

ALVA B. CLARK, OF BROOKLYN, NEW YORK, ASSIGNOB TO AMERICAN TELEPHONE AND TELEGRAYH COMPANY, A. CORPORATION OF NEW YORK.

. TELEPHONE AND CALL SIGNAL SYSTEM.

Application filed September 20, 1918. Serial To all whom it may concern:

Be it known that I, ALVA B. CLARK, residin at Brooklyn, in the county of Kings and tate of New York, have invented certain Im iovements in Telephone and Call Signal ystems, of which the following is a specification.

This invention relates to signaling systems in which it is desired to transmit currents of difierent frequencies at different times, as, for instance, the talking and ring ing frequencies in a telephone circuit. The object of the invention is to make thecircuit eihcient for transmitting currents of either frequency.

Transmitting circuits containing transformers, or other localized inductance, are usually designed to transmit most efliciently the particular range of frequencies which it is expected to employ, and a circuit so designed isrelatively inefficient for transmitting other frequencies. The efiiciency of the circuit for transmitin those other frequenci s can, however, be c anged by connecting into it, in suitable relation, other elements of inductance or capacity, or by changing the value or relation of existing elements. In general, my invention consists in providing means responsive to the change in the frequency transmitted over the circuit for varying the character of the circuit to make it eihcient with respect to the frequency being transmitted. It is here illustrated as applied to a telephone amplifier circuit for al tering its condition when the ringing current is transmitted, and has been found especially useful in this relation but it will be understood that the invention is not limited to use in circuits of this particular character, or even to telephone circuits in general.

For a fuller understanding of the invention reference will be made to the accompanying sheet of drawings in which Figure 1 represents diagrammatically a telephone repeater circuit embodying the invention, and Fig. 2 shows curves illustrating the operation.

The amplifier 1 is here illustrated in its typical form, having transformers 2 and 3- in the input and output circuits respectively, the transformer 2 connecting with the incoming line 4., and transformer 3 with the outgoing line 5. An adjustable resistance 6, sometimes known as a potentiometer is connected Specification of Letters Patent.

into the incoming line 4, and serves to adust the amount of amplification. It consists of a resistance connected across thecircu1t with provision for connecting thecontinum line conductor to any deslred point thereo whereby part of the resistance will, n general, be in series with the line and part in shunt. It is here shown ascompris' two sections, one on either side of the line, this being merely for the purpose of preserving the balance.

The operation of the circuit as thus far described is indicated by curve a in Fig. 2, where amplification is plotted against frequency. The frequencies comprised within the talking range will be those lying between the dotted lines as and y. it will be observed that the amplification for the talking currents is very considerably above thosewithin the ringing range as, for example,l33 cycles, indicated "by the line a. This higher Neillciency for the higher frequencies is due largely to the design of the retardation coil.

15 and the transformers 2 and 3 particularly the input transformer 2. It is necessary to add materially to the cost of these input transformers to make them as efiicient for the low frequencies as for the high frequencies. Furthermore, itis at times desirable that these transformers be inefiicient at low frequencies in order to avoid interference from extraneous currents of low frequency, as for example, interference from Morse currents when thetransmission circuit is used simultaneously for the transmission of Morse messages and telephone conversation.

To overcome this difliculty, I provide a condenser 7 to be connected across the circuit at the terminals of the transformer 2 former 2 across which it is bridged, it constitutes a tuned circuit at the ringmg frequency. The shunt containing the condenser is provided with a normally open switch 8. A'switch 9 is provided-for opening the potentiometer circuit when the condenser circuit is closed, and both of these switches are operated by a magnet 10 whose circuit is controlled by the relay 11, connected, preferably into the output circuit of the amplifier 1 and across the terminals ofa condenser 12. A condenser 14. is alsoconnected in series with the relay 11 to prevent the flow of direct current through it.

Patented Mar..15, 192 1.

9 5 value is such that, with the winding of transexample 133 cycles, is transmitted, it will,

because of its lower frequency, find a ready path through the relay winding 11 and condenser 14 whose capacit is such as to make it resonant, with the re ay winding, for the ringing frequency; while the condenser 12, will present a higher impedance than at talking frequencies. The ringing current will, therefore, cause the contact 13 of the relay 11 to chatter, which will so reduce the current traversing the winding of relay 10 that it will release both of the switches 8 and 9, thus opening the circuit of turpetentiometer 6 and connecting the condenser 7 across the line. The opening of the shunt, which the potentiometer circuit normally forms causes an increase in the voltage across the terminals of the transformer 2 for reasons which will be obvious, and the closing of the condenser shunt, which completes the local circuit tuned to the ringing frequency, greatly augments this increase by reason of the high impedance which the local circuit then presents in comparison with the rest of the circuit extending to the current source.

The efliciency of the transmission lines at the ringin frequency, and particularly of the ampl' er circuit, is thus greatly increased. The effect of the alteration of the circuit, asabove described, is indicated by the curve 6 in Fig. 2. The resulting amplification of the ringing current can be made not only equal to, but evengreatgr than, the amplification of the talking currents during normal line conditions, as indicated by the sharp rise of the curve b at the line 2.. On the other hand, the amplification for the frequencies within the talking range are considerably reduced, as indicated by the drop at the tail of the curve I). I

The amplification of the ringing current can be adjusted to be equal to, or to have.

any ratio desired to the amplification of the talking currents during normal line condi tions by connecting a resistance 16 of suitable value in series with condenser 7. Asv

above indicated,it is preferable, though notessential to the invention, to connect the relay 11 in the output circuit of the amplifier, because even before the circuit conditions are changed, the ringing current is somewhat strengthened by the amplifier 1, and therefore, more-readily affects the relay. This will be clear from the fact that the curve a crosseszthe line a somewhat above the zero line. I

It will be obvious that the invention, when used in connection with' an amplifier, may be applied to one-way repeaters, used in use. The invention is obviously applicable to circuits other than amplifier or repeater circuits, and it will be manifest that the invention is not limited to the particular arrangement herein disclosed, as various modifications in details falling within the spirit and scope of the invention, will suggest themselves to those skilled in the art.

What is claimed is:

1. In a signaling system, a circuit designed to transmit currents of certain frequencies, a relay associated with said circuit which is unresponsive to currents of said frequencies, but responsive to currents of a different frequency, and means controlled by said relay for changing the characteristics of the circuit to make it more efficient for transmitting currents of said different frequency.

2. In a signaling system, a repeater circuit including input and output transformers, and designed for maximum amplification of certainfrequencies, a relay associated with said circuit which is unresponsive to currents of said frequencies, but responsive to currents of a d ifierent frequency, and means controlled by said relay, for changing the characteristlcs of said repeater circuit to make it more eflicient for transmitting currents of said different frequency.

3. In a signaling system, a circuit dei frequency.

' signed, is transmitted over the line to change the constants of said circuit whereby it is more eflicient in transmission for such other frequency. 1

5. In a signaling system, circuit designed to transmit most efiiciently currents of certain frequencies including a. resistance,

part of whichis arranged in a shunt across said circuit, a condenser connected in anopen shunt across said circuit, and means for opening the shunt including the resistance, and for closing the shunt including the condenser, when the current of a frequency other than those for which the cirizuit 1s so designed, is transmitted over the me. Y

6. Iiia signaling system, a repeater circuit designed for most eificient transmlssion of currents of certain frequencies, comprising an amplifier, input andmutput circuits for said amplifier including transformers, means associated with the input transformer for rendering said re eater eflicient for frequencies other than t ose for which the cir-,

cuit is so designed, and mechanism responfrequencies, a condenser connected in an open circuit across said transformer, and having a value to make it resonant w1th the transformer winding at a frequency other than those for which the circuit is so designed, and means responsive to said other frequency to open the resistance circuit, and to close the circuit of the condenser.

8. In a signaling system, an amplifier having input and output circuits, and designed for a maximum amplification of cur-. rents of certain frequencies, a relay in the output circuit of said amplifier unresponsive to currents of sald fre uencies, but responsive to currents of a di erent frequency, and

means controlled by said relay for giving said amplifier maxlmum efliciency for currents of. said other frequency.

In testimony whereof I have signed my name to this specification this eighteenth day of September, 1918.

ALVA B. CLARK. 

